Treatment of rubber to form bituminous compositions

ABSTRACT

The present invention provides a procedure for at least partial dissociation of crumb rubber vulcanate network, including automobile tires, and for the incorporation of this treated rubber into stable bitumen compositions. The at least partially dissociated rubber vulcanate network may be used independently as a bitumen modifier, or a stabilizing agent for ground vulcanate rubber dispersions in bitumen or as a steric stabilizer in dispersion of polyolefins in bitumen. The at least partially dissociated rubber vulcanate network materials are produced in situ in bitumen or produced separately and subsequently incorporated into bitumen and the bituminous compositions are useful materials for a variety of applications. Modifications are possible within the scope of this invention.

FIELD OF INVENTION

The present invention relates to the treatment of vulcanate rubber,particularly scrap rubber from automobile tires as well as from othersources, to effect partial or high levels of dissociation of the rubbervulcanate network and the incorporation of such treated rubber intostable bituminous compositions.

BACKGROUND TO THE INVENTION

Motor vehicle tires represent a significant disposal problem andattempts have been made to recycle the same, for example, byincorporation of recycled ground rubber formed from such tires intovarious products, including asphalt compositions for roadway pavements.Such ground rubber is often identified by the term "rubber crumb" andthat expression is employed herein.

Recycled rubber crumb generally contains a variety of rubber polymers,including styrene-butadiene rubber, natural rubber and its syntheticanalog (cis-polyisoprene), cis-polybutadiene, butyl rubber and EPDMrubber. Often such recycled rubber crumb comprises predominantlystyrene-butadiene rubber.

A search of the prior art in the facilities of the United States Patentand Trademark Office has located the following United States patentsrelated to the reclaiming of rubber from vulcanized rubber waste,including automobile tires:

    ______________________________________                                               1,168,230     1,133,952                                                       1,981,811     2,645,817                                                       3,880,807     3,896,059                                                       4,161,464     4,146,508                                                       4,469,817     5,095,040                                                ______________________________________                                    

These patents relate to a variety of mechanical, chemical and mixedmechanical and chemical procedures.

Crumb rubber generally is recycled rubber that has been reduced toground or particulate form by mechanical shearing or grinding. A varietyof procedures have been used to reclaim materials from ground scraprubber, one of the most common being an alkali process in which groundrubber is treated in aqueous sodium hydroxide solution at elevatedtemperature. Other reclaiming processes involve treatment of groundrubber in processing oils using various combinations of high temperatureand excessive shear for the purpose of producing liquified materialswhich may be incorporated into the manufacture of new tires or useddirectly as fuel oil.

In addition, it has been proposed that scrap crumb rubber beincorporated into asphalt paving materials. In general, crumb rubber maybe incorporated into asphalt paving materials by one of two processes,namely a wet process or a dry process.

In the wet process, the crumb rubber is blended into the asphalt cement,by batch blending in which batches of crumb rubber and asphalt are mixedin production, by continuous blending with a continuous productionsystem, or by terminal blending. An asphalt cement binder that has beenmodified with crumb rubber is termed asphalt rubber. In the dry process,the rubber crumb is added to heated aggregate, not the asphalt cement,or hot mix asphalt mixture during production of the mix.

In one such wet procedure, hot asphalt (about 190° to 220° C.) is mixedwith approximately 25 to 30 wt % crumb and the mixture then is dilutedwith kerosene. A variation of this procedure uses about 22 wt % crumbwith dilution being effected using extender oil. It is thought thatblending the crumb rubber and asphalt at elevated temperature maypromote limited chemical bonding of the components. However, thesecompositions exhibit only short-term stability and, therefore, must beemployed shortly after formation.

A recent variation of the wet process is contained in U.S. Pat. No.4,992,492. The process involves a mixture of asphalt or sulfur-treatedasphalt (81 to 86%), crumb rubber (8 to 10%), extender oil (4 to 6%) anda high molecular weight (>100,000) olefinically-unsaturated syntheticrubber (2 to 3%) which is blended together at 175° to 180° C. for abouttwo hours.

As claimed, this process differs from the present invention in a numberof important facets. In the referenced process the ground crumb rubberis dispersed in the bitumen, however, the vulcanate network undergoeslimited, if any, chemical disassociation. Such crumb rubber compositionswould be unstable without the incorporation of the claimed high MW(≧100,000) olefinically unsaturated synthetic rubber. The high MW freesolvated synthetic rubber chains likely act to minimize changes inviscosity and softening point over periods of up to 10 days in "ahermetically-sealed vessel without agitation at 160° to 165° C.".

In recently-published WO 93/17076, ground rubber particles are heavilyoxidized, particularly at the surface of the particles, with airinjected under pressure at a high temperature (220° to 260° C.), in aprocedure similar to that employed conventionally for producing anoxidized or "blown" asphalt for roofing-grade asphalt. Such treatment ofthe fine rubber particles in situ improves desired rubber dispersibilityand compatibility, but also may impart undesirable brittleness to theasphalt matrix.

The incorporation of crumb rubber from recycled automobile and othertires into bitumen or asphalt is desirable in view of the potentiallyimproved properties of composition attained thereby and the recycle ofscrap rubber achieved thereby.

SUMMARY OF INVENTION

In accordance with the present invention, partial or high levels ofdissociation of rubber crumb network, particularly crumb rubber fromrecycled automobile tires, or other sources of scrap rubber, is effectedand the incorporation of the products of such treated rubber intobitumen to produce stable bituminous materials useful in a variety ofapplications, as described in more detail below, thereby incorporatingthe original scrap rubber into useful products. In particular,particulate rubber material may be dispersed in bitumen in a mannerwhich resists separation of a stable dispersed particulate rubber phase,particularly provided by crumb rubber from recycled automobile tires.

According to one aspect of the invention, there is provided a method offorming a bituminous composition, which comprises mixing rubbervulcanate particles with a hydrocarbon oil to effect softening andswelling of the rubber particles, applying thermal energy and mechanicalenergy to the softened and swollen particles to effect at least partialdissociation of the vulcanate network, dispersing the at least partiallyliquified rubber particles in bitumen, providing at least onecompatibilizing agent in the bitumen to incorporate treated rubber fromthe at least partially dissociated rubber vulcanates into the bitumen,and, if necessary, cross-linking the compatibilizing agent, bitumen andtreated rubber including any residual rubber particles to stabilize theresidual rubber particles against separation from the bitumen bysedimentation.

The present invention also provides, in another aspect, a bituminouscomposition comprising a continuous bitumen phase and a dispersed phasecomprising dissociated rubber vulcanate network. Such composition thenmay provide the vehicle for providing a bituminous compositioncontaining a dispersed phase, including rubber particles, which may bepartially dissociated as described herein, or particulate polyolefins,in which case the particles are stabilized against separation from thebitumen by cross-linking.

In a further embodiment of the present invention, the at least partiallydissociated rubber vulcanate network may be used as a steric stabilizerto prevent phase separation of dispersed polyolefins from hot liquidasphalt.

GENERAL DESCRIPTION OF INVENTION

The term "bitumen" used herein has its conventional technical meaningand means a class of black or dark-colored (solid, semi-solid orviscous) cementitious substances, natural or manufactured, composedprincipally of high molecule weight hydrocarbons of which asphalts,tars, pitches and asphalites are typical. The term "asphalt" as usedherein has its conventional technical meaning and means a dark, brown toblack, cementitious material, solid or semi-solid in consistency, inwhich the predominant constituents are bitumen that occur in nature, assuch, or are obtained as residue in petroleum refining. The bituminousmaterial employed herein may arise from a variety of sources, includingstraight and vacuum residue, mixtures of vacuum residue with a varietyof diluents, including vacuum tower wash oil, paraffin distillate andaromatic and naphthenic oils. Other aspbaltic materials, such as rockasphalt, naturally-occurring asphalt and coal tar pitch, also may beused.

The procedure of the present invention is applicable to any rubberproduct, whether synthetic or natural, vulcanized or non-vulcanized, andmay be applied to one-component rubber materials or mixtures of two ormore rubbers. The invention is particularly described for economicreasons with respect to crumb rubber from recycled automobile tires froma variety of sources, including whole tires, tires treads, tire baffins,whether automobile or truck tires, as well as from other industrial orcommercial rubber waste.

The particle size of the crumb rubber which is processed herein may havea wide range, for example, from about % inch to about 200 mesh. Scrapautomobile tire crumb conveniently may be sized from about 10 to about80 mesh for utilization in the process of the invention. Preferably, thecrumb rubber used in the invention is derived from recycled automobiletires and hence may comprise significant amounts of vulcanized syntheticstyrene-butadiene rubber.

The crumb rubber is mixed with asphalt containing a hydrocarbon oil, asa swelling agent, and a synthetic liquid rubber, as a compatibilizer.Three different, yet related, embodiments of the present invention areprovided. Each such embodiment may be effected by two alternativemethods, one more preferred than the other. In the more preferredalternative, the process is carried out wholly in bitumen while in theless preferred alternative, the crumb rubber is processed separatelyfrom bitumen and only after processing are the products of suchprocessing incorporated into bitumen.

In the alternative where the processing of the crumb is effected inbitumen, the bitumen itself may contain sufficient hydrocarbon oilcomponent to effect the softening and swelling such that no furtherhydrocarbon oil need be added. In general, the hydrocarbon oils employedin the present application are those derived from petroleum or coal tarwhich are compatible with the products of the dissociation. The usefulhydrocarbon oils may be variously described as naphthenic, aromatic orparaffinic, depending on the predominant structure of the oil.Preferably, the hydrocarbon oil employed has a high aromaticity, sincesuch characteristic facilitates penetration of the oil into the surfaceof the crumb rubber particles and the softening and swelling of thestructure. Particular aromatic oils which may be used herein includethose available under the trade-names "SUNTEX" 790 AND 780T and"HYDROLENE" 80T, 90 and 125.

The crumb rubber is loaded in the bitumen containing the hydrocarbon oilover a wide concentration, generally from about 5 to about 75 wt %,which loading may be effected at one time or incrementally duringprocessing of the crumb rubber. Generally, when the crumb rubber isdispersed in the bitumen hydrocarbon oil mixture at elevated temperature, some of the oil is taken up by the crumb rubber as penetration of thecrumb rubber by the oil occurs. The quantity of crumb rubber which maybe mixed initially with the oil should be such that a continuous oilphase remains following the initial mixing. The amount of hydrocarbonoil in the hydrocarbon oil/bitumen mixture may vary according to severalfactors, such as the level of oil present in the bitumen, desiredperformance characteristics and level of crumb rubber to be treated.

The crumb rubber particles then are subjected to thermal and mechanicalenergy to commence breakdown of the vulcanized rubber particles, throughbreakdown of sulfur--sulfur bonds and cross-links between polymermolecules. This process increases the solubility and compatibility ofthe at least partially dissociated rubber vulcanate network into thebituminous phase and also promotes the dissolved free liquid rubberchains, added as a compatibilizer, to chemically combine in-situ withthe at least partially dissociated rubber vulcanate network. Theconditions used for the dissociation of the vulcanized rubber particlesdepends on a number of factors, as discussed below. In particular, thetemperature may range from about 100° to about 300° C. with mechanicalenergy being applied by shearing at a shear rate which may varysignificantly depending on other processing parameters. For example,processing of the ground crumb rubber at lower temperatures may requireuse of higher shear rates while lower shear rates may be possible atmore elevated temperatures. The heat and mechanical energy being appliedover a period of time which may vary widely, from about 15 minutes toabout 8 hours or more, depending on the components employed, processingparameters and the nature of the product desired.

In general, the process according to the present invention to effect atleast partial dissociation of the crumb rubber vulcanate network iscontrolled by a number of variable factors, including type ofhydrocarbon oil, initial concentration of oil in bitumen, processconditions employed, such as equipment type, shear rate, temperature andthe interrelation of shear rate and temperature, the use of additionaldevulcanization agents, the timing of addition of crumb rubber, size andloading rates, amount and timing of addition of a cross-linking agent,as discussed below, and the molecular weight and type of the liquidrubber, as well as the functionality of the rubber, if applicable. Byutilizing this combination of parameters, the degree of dissociation ofthe scrap rubber may be controlled to produce a variety of products, asdescribed below.

The liquid rubber component employed in the present invention is highlysoluble or highly compatibilized with liquid bituminous compositionsunder typical processing conditions, generally about 100° to 300° C.,preferably about 150° to about 220° C. Such liquid rubber can serve tocompatibilize bitumen with the ground rubber and also tends to penetratethe oil swollen crumb rubber and facilitate its mixing into the asphalt,thereby facilitating the in-situ chemical bonding of the liquid rubberwith the at least partially dissociated rubber vulcanate network throughfree-radical chain transfer reaction.

Such liquid rubber may be functionalized or non-functionalized andpreferably has a molecular weight in the range of about 300 to about60,000 and preferably has a similar molecular structure (i.e.polybutadiene, polyisoprene or styrenic copolymers derived therefrom) tothe scrap rubber in order to facilitate the physical and/or chemicalincorporation of the at least partially dissociated rubber vulcanatenetwork into the bitumen.

If a functionalized liquid rubber is used, the functional group may bean amine, diol, maleic anhydride, cyanide, carboxylic acid or sulfonate.Of such functional groups, amines are preferred, since such organicgroups contain which, due to their basicity, can act as a catalyst toaccelerate the dissociation process and also assist in the couplingreaction required to link other dispersed polymer particles, such aspolyolefins, preferably polyethylene, if such particles are present inthe bituminous composition.

When the process is carried out in bitumen having a low hydrocarbon oilcontent, it is preferred for the liquid rubber to be dissolved in thebitumen at the start of the process, although the liquid rubber may beadded at any convenient stage of processing of the bitumen/rubberparticle composition. When the process is carried out in hydrocarbon oiland then the at least partially dissociated rubber vulcanate network isadded to bitumen, the liquid rubber usually also is added to the bitumenat the same time. In general, the amount of liquid rubber employed isabout 0.01 to about 10 wt %, preferably about 0.1 to about 3 wt % of thebitumen.

The application of heat and mechanical energy to the dispersed swollencrumb rubber particles in the bitumen causes dissociation of the rubbervulcanate network and a continuous reduction in the rubber vulcanateparticle size, the degree of particle size reduction depending on thelength of time for which the thermal and mechanical energy are appliedto the composition, in addition to the other process parametersdiscussed above. If such processing is effected for a sufficientduration, all the rubber particles become dissociated, so that thereremain no discernible rubber particles in the composition.

However, if such processing is effected for a sufficient duration andwithout sufficient control that the rubber vulcanate network is heavilydissociated, an oil-like liquified material is produced, which may notbe desirable for use in paving and roofing related applications. Suchoil-like liquified materials may be better suited for use as a diluentin asphalt and non-asphalt based coatings and sealants.

Crumb rubber from automobile tires generally contains a significantproportion of carbon black. The dissociation procedure used herein tendsto cause a release of carbon black particles. Typically, such carbonblack particles would separate from the continuous bitumen phase, bymeans of sedimentation.

In the present invention, the stability of the released carbon black isimproved through the surface grafting of the liquid rubber and the atleast partially dissociated rubber vulcanate network onto theseparticles during free radical chain transfer reaction.

In general, the highly dissociated material may be dispersed in bitumenand remain in the liquid phase solely through the use of the liquidrubber component. However, at intermediate stages between thecommencement of dissociation and the highly dissociated material wherethere remain dispersed degraded rubber particles, in order to provide astable dispersion of such degraded rubber particles in bitumen, it isnecessary for chemical reaction to be effected by way of cross-linkingof the liquid rubber, in order for the degraded rubber particles to bestabilized against sedimentation from the bitumen.

An important aspect of the present invention is the ability to controlthe degree or level of dissociation of the rubber vulcanate network.Materials of certain levels of disassociation may be used independentlyor advantageously combined together.

The highly dissociated rubber vulcanate network which has beensolubilized or compatibilized in the bitumen can subsequently bere-vulcanized in-situ through the use of commonly employed cross-linkingagents. This revulcanized modified bitumen exhibits improved elasticityand stiffness without risk of phase separation due to irreversiblechemical bonding into the bitumen.

Such cross-linking and/or grafting may be effected using any convenientcross-linking agent, including sulfur, sulfur donor, with or withoutaccelerating additives, and other free-radical initiators, such ashydrogen peroxide. In general, the amount of cross-linking agentemployed is about 0.05 to about 5 wt %, preferably about 0.2 to about 3wt % of bitumen. The cross-linking agent may be added at any convenientstage of processing.

In another embodiment of the inveniton vulcanized crumb rubber particlesmay be added and incorporated into the above described highlydissociated rubberized asphalt composition. In such compositions the atleast partially dissociated rubber network may chemically bind on thesurface of the rubber vulcanate particles thereby creating stablecompositions.

A stable bitumen composition is produced in the preferred aspect of theinvention in which no phase separation of residual degraded crumb rubberfrom automobile tires and carbon black released from crumb rubber by thedevulcanization occurs at elevated temperatures, generally in the rangeof about 100° to about 300° C.

Incremental loadings of crumb rubber particles may be employed toprovide a very high loading of dispersed stabilized rubber in theproduct bitumen composition, generally in the range of about 25 to about80wt %. Such concentrated material, or masterbatch, may be diluted withbitumen to form a composition containing a desired concentration ofstabilized crumb rubber, generally in the range of about 3 to about 40wt %, for a variety of asphalt applications, including all types ofpaving, preformed paving bricks, roofing membranes, shingles,waterproofing membranes, sealants, caulks, potting resins and protectivefinishes. Alternatively, such masterbatch may be compounded with fillersand/or polymers and the compounded composition may be pelletized toproduce a pelletized composition for subsequent incorporation intoasphalt compositions for such uses.

In our published International patent application WO 93/07219 thedisclosure of which is incorporated herein by reference, there isdescribed the provision of stable asphalt compositions in whichpolyethylene particles are maintained as a dispersed phase by stericstabilization. As described therein, the bitumen comprises the majorcontinuous phase of the polymer-modified bitumen compositions and thepolymer is dispersed in the bitumen by steric stabilization achieved bya first component anchored to the polymer phase and a second componentbonded to the first component and soluble in the bitumen.

In addition, as described in copending UK patent application No.9306517.5 filed Mar. 29, 1993, in the name of Polyphalt Inc, additionalhomopolymer or copolymer component, including styrenic copolymers,olefinic copolymers and E-P rubbers may be provided in the bitumencomposition, in the form of particle dispersions, strand-likedispersions, solutions and combinations in which the additionalhomopolymer and copolymer components are stabilized against separation.

The at least partially dissociated rubber vulcanate network produced inthe manner described above may be added, as is or stably dispersed inbitumen, to these bitumen compositions so that the residual rubber crumbparticles form part of the stable dispersed phase and may providesupplementation to or partial replacement for the polyethylene or otherpolymer particles. The unsaturated components of the liquid rubber andsuch at least partially dissociated rubber vulcanate network may beemployed to replace polybutadiene-based stabilizer, in whole or in part,as the steric stabilizer. If the unsaturated rubber, used in theproduction of the at least partially dissociated rubber vulcanatenetwork is functionalized, then this unsaturated rubber can be used toreplace the second component which is bonded to the first component andanchored to the dispersed polymer, as described above.

The formation of stable dispersions of crumb rubber in bitumen by theprocedure employed herein may be combined with stabilization ofdispersed polyethylene and other olefinic polymers and copolymers, asdescribed above, to improve the characteristics thereof. Pavingmaterials generally include aggregate, such as crushed stone pebbles,sand etc, along with the bitumen composition. Similarly, other additivesto the bitumen composition may be employed, dependent on the end use towhich the bituminous composition is put. For example, a roofing materialmay be obtained by the addition of suitable fillers, such as asbestos,carbonates, silica, wood fibres, mica, sulfates, clays, pigments and/orfire retardants, such as chlorinated waxes. For crack-fillerapplications, an oxide may be advantageously added.

EXAMPLES Example 1

This Example illustrates the processing of rubber crumb to a dissociatedrubber vulcanate network and the incorporation of such treated rubberinto an asphalt composition.

Automobile tire rubber crumb of 20 mesh size was mixed with the aromaticoil "SUNTEX" 790. This oil is characterized by the physical and chemicalproperties shown in the following Tables I and II:

                  TABLE I                                                         ______________________________________                                        Viscosity Range         MED                                                   ______________________________________                                        Physical Properties ASTM    790                                                                   Method                                                    Viscosity, SUS/100° F.                                                                     D2161   3500                                              Viscosity, SUS/21O° F.                                                                     D2161   96.3                                              API Gravity, 60° F.                                                                        D287    11.0                                              Specific Gravity, 60° F.                                                                   D1250   0.9979                                            Viscosity - Gravity Constant                                                                      D2501   0.954                                             Weight, lb/cal      D1250   8.27                                              Molecular weight    D2502   398                                               Pour Point, °F.                                                                            D97     +70                                               Volatility - Wt. % @ 225° F.                                                               D972    1.2                                               Flash Point, COC. °F.                                                                      D92     420                                               Refractive Index    D1747   1.5684                                            Aniline Point       D611    97                                                ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Clay-Gel. Wt. 5%   D2007                                                      Asphaltenes            0.1                                                    Polar Compounds        10.4                                                   Aromatics              73.2                                                   Total Aromatics        83.6                                                   Saturates              16.3                                                   Carbon Type Analysis, %   D2140                                               Ca                     37                                                     Cn                     28                                                     Cp                     35                                                     ______________________________________                                    

Following an initial loading of 15 wt % of rubber crumb to the oil (i.e.a mixture of 15wt % rubber crumb, 85 wt % oil), the mixture was heatedto about 180° C. under high shear conditions using a Brinkman Polytronhigh shear mixer with a 45H mixing head. Initially, the viscosity of thecomposition increased and then started to fall after about 20 minutes asdissociation of the oil swollen rubber network commenced. At this point,a loading of a further 10 wt % rubber was added to the liquid mass andthe application of heat and shear forces continued. During the mixing,the temperature of the composition rose to a range of about 200° to 250°C. as a result of friction forces. The application of heat and shearforces continued for about 3 hours, at the end of which time the rubbervulcanate was heavily dissociated and dissolved in the oil. A furtherloading of 10wt % of rubber was added and the procedure repeated. At theend of about a further 0.5 hours, there was provided a highly dissolvedmass comprising 35 wt % liquified rubber crumb and 65 wt % aromatic oil.

The procedure was continued employing a high shear which resulted inmore and more incrementally added crumb rubber up to 65 wt % rubbercrumb which was dissociated into aromatic oil solution, formed in about6 hours.

To the treated rubber comprising 65wt % of dissolved rubber crumb and 35wt % aromatic oil were added polybutadiene rubber (Ricoh 134, ColoradoChemical Specialities Inc. Microstructure 80% trans- and cis-1,4; 20%1,2-vinyl, molecular wt (MW=12,000) in an amount of about 3 to 5 wt % ofthe amount of treated rubber crumb and sulfur in an amount of about 1 wt% of the amount of treated rubber crumb to the oil, and the resultingmixture was heated for about 1 hour at that temperature to form across-linked material.

The resulting cross-linked material was mixed with liquid asphalt(Petro-Canada Bow River, Penetration 85/100, see Table III below forproperties) in an amount of 20 to 40% by weight of mixture to provide acompatible composition.

The asphalt/cross-linked material mixture was mixed with a stabilizedasphalt composition as described in WO 93/07219 based on asphalt (ColdLake 300 to 400 penetration) at an elevated temperature of 160° C.containing 4 wt % dispersed sterically-stabilized polyethylene and 2wt %polybutadiene. The asphalt/cross-linked material was added in amountcorresponding to 2.5 wt % of the treated rubber crumb in thecross-linked material, for a total polymer content of the asphaltcomposition of 7.5 wt %.

Upon examination of the resulting asphalt composition, it was observedthat the particle size of the polyethylene particles was decreased andthe dispersion of polyethylene particles was more uniform in size thanin the composition prior to addition of the asphalt/cross-linkedmaterial mixture. In addition, the elastic properties of the asphaltcomposition were enhanced.

Example 2

This Example provides a comparative Example using the conventional stepsaccording to wet process.

In a 1 L mixing vessel, 84 parts of asphalt (Petro-Canada Bow River,Penetration 85/100, see Table III below for properties) were heated to180° C. 10 wt % of crumb rubber (Baker Rubber Inc., 20 mesh) and 6 partsof aromatic oil (Sunrex 790, see Tables I and II above for properties)were added into the asphalt and dispersed under high shear (with aBrinkman Polytron Mixer for 2 hours at 180° C. to 240° C.

                  TABLE III                                                       ______________________________________                                                                   Bow River                                          Property           ASTM    85/100                                             ______________________________________                                        Viscosity at 135, CP                                                                             D4552   400                                                Specific Gravity at 15° C.                                                                D1298   1026                                               Molecular Weight g/mol                                                                           D2502   1200                                               Compositions (%)   D2007                                                      Asphaltenes                10.3                                               Total Aromatics            71.1                                               Saturates                  18.5                                               ______________________________________                                    

The mixture was stored in an oven at elevated temperature (at 140° C.)for 48 hours without agitation. Inspection of the mixture at the end ofthis period showed that almost all the crumb rubber which had beendispersed into the asphalt had sedimentated at the bottom section of thevessel. The viscosity of the asphalt at the bottom of the vessel wasmuch higher than that at top. Such a rapid phase separation (or crumbrubber sedimentation) is seen from the storage stability test data inTable IV below.

Example 3

Example 2 was repeated except that 10 parts of 20 mesh crumb rubber wasreplaced by 10 parts of 40 mesh crumb rubber. The finer ground-up tirerubber used still tended to rapidly separate or sediment into a crumbrubber layer at the bottom of the vessel. The result is shown in TableIV.

Example 4

This Example illustrates the formation of a stable bitumen-ground rubbercomposition in accordance with the invention.

6 parts of the aromatic oil (Suntex 790) was mixed with 4 parts ofasphalt (Bow River 85/100) at 150° C. To the asphalt were graduallyadded 10 parts of crumb rubber (20 mesh) and 0.8 part of polybutadienerubber (Ricon 131, Colorado Chemical Specialities Inc. Microstructure80% trans- and cis- 1,4, 20% 1,2-vinyl, molecular weight (Mw)=5,500) insequence and mixed under high shear (with a Brinkman Polytron Mixer) ata temperature between 180° C. and 240° C. for 2 hours. To this stirredmixture was added 80 parts of additional asphalt (Bow River 85/100) andthe resulting mixture was further mixed at 180° C. for 0.5 hour to forma stable ground tire rubberized asphalt composition. After 2 daysstorage at 140° C., the viscosity of the binder showed no appreciablechange with respect to the binder before storage and essentially nodifference between the top and bottom in the vessel, which indicatedthat the liquified rubber remained dispersed in the bitumen. The testdata is shown in Table IV.

Example 5

Example 4 was repeated except that 6 parts of the crumb rubber wereadded to the bitumen along with the aromatic oil and the polybutadieneat first and mixed for 2 hours and then 4 parts of additional crumbrubber plus 0.2 part of elemental sulfur were incorporated into themixture. 80 parts of additional asphalt was added to the high shearstirred mixture after dispersing the added crumb rubber for 15 to 20min., when the viscosity of the mixture went obviously up. Some of thecrumb rubber particles remained dispersed in the asphalt and theresulting asphalt composition stable after two days storage at 140° C.(see Table IV)

Example 6

The procedure of Example 4 was repeated, except that 1 part of sulfurwas added after 2 hours mixing of the same crumb rubber as employed inExample 3 and mixed for one hour at 180° C. to form a gel-like materialwhich was still readily dispersed and compatible with the asphalt, toproduce a stable rubber asphalt binder with the same composition as inExample 4. The resulting asphalt rubber was quite stable at elevatedtemperature (see Table IV).

Example 7

The procedure of Example 4 was repeated, except that the mixtureproduced in Example 4 was treated with 1 part of sulfur at elevatedtemperature around 180° C. for one hour. The solubilized or devulcanizedrubber in the asphalt composition was revulcanized in situ by thecross-linking reaction to form a smooth asphalt composition withoutphase separation. The resulting composition had an excellent stability.(see Table IV).

Example 8

This Example illustrates the incorporation of polyethylene into thestable asphalt-rubber crumb composition.

Example 4 was repeated except that 0.8 parts of liquid polybutadiene wasreplaced by 0.8 part of amine-terminatedPoly(butadiene-co-acrylonitrile) (10% acrylonitrile, in liquid form, BPGoodrich, amine equivalent weight=879 g/mole). To the mixture produced,1 part of maleic anhydride grafted polyethylene (Dupont Fusabond D-110,density at 25° C.=0.920 g/mol, melt index--40) and 0.8part of sulfurwere added in order and mixed at 180° C. in the Polytron high shearmixer for 1 hour. Then, 4 parts of recycled polyethylene (low densitypolyethylene, melt index, 5) were dispersed into the stirred mixture at180° C. for 30 min., forming a homogeneous asphalt composition. Therecycled polyethylene was stabilized in the crumb rubberized asphaltbinders at elevated temperature, no phase separation from the bitumen ofeither the dispersed polyethylene particles or the crumb rubber phasewas observed, as evidenced by microscopic observation on the sampleafter storage at 140° C. for 48 hours.

Example 9

The process of Example 8 was repeated except that the 10 parts of crumbrubber which had been solubilized or devulcanized during mixing processdescribed in Example 4 were omitted. The resulting composition wasunstable against polyethylene coalescence from asphalt at elevatedtemperature, as evidenced by the microscopic observation as described inExample 8.

                                      TABLE IV                                    __________________________________________________________________________                   Example                                                        Component, phr 2  3  4   5  6   7  8                                          __________________________________________________________________________    Asphalt (Bow River 85/100)                                                                   64 64 84  84 84  64 84                                         Suntex 790     6  6  6   6  6   6  6                                          Crumb rubber   10 10 10  10 10  10 10                                         Liquid Polybutadiene                                                                         -- -- 0.8 0.8                                                                              0.8 0.8                                           Sulfur         -- -- --  0.2                                                                              1.0 1.0                                                                              0.8                                        Maleic Anhydride-g-polyethylene                                                              -- -- --  -- --  -- 1.0                                        ATBN rubber    -- -- --  -- --  -- 0.8                                        Recycled Polyethylene                                                                        -- -- --  -- --  -- 4                                          Viscosity (CP)*, Brookfield                                                   at 135° C., 20 rpm                                                     at Top Section 545                                                                              675                                                                              537.5                                                                             575                                                                              667.5                                                                             900                                                                              --                                         at Bottom      2975                                                                             3100                                                                             555 650                                                                              675 837                                                                              --                                         Stability      No No VG  VG VG  VG VG                                         __________________________________________________________________________     Note: VG = Very Good                                                          Viscosity of the crumbasphalt binders after storage at 140° C. for     46 hours.                                                                

We claim:
 1. A method for forming a bitumen composition, whichcomprises:mixing rubber vulcanate particles with a hydrocarbon oil toeffect softening and swelling of the rubber vulcanate particles,applying thermal energy and mechanical energy to said softened andswollen particles to effect at least partial dissociation of a rubbervulcanate network of the rubber vulcanate particles, dispersing said atleast partially dissociated rubber vulcanate network in bitumen havingat least one compatibilizing agent therein sufficient to incorporatetreated rubber from said at least partially dissociated rubber vulcanateinto said bitumen, and effecting said thermal energy and mechanicalenergy application step until the rubber vulcanate particles have becomedissociated to the extent that there is no discernible dispersed phaseof rubber vulcanate particles as determined by the absence ofsedimentation of rubber vulcanate particles after storage of saidbitumen composition at 140° C. for 2 days.
 2. The method of claim 1wherein said dispersing of said at least partially dissociated rubbervulcanate network in bitumen is effected by effecting said mixing andenergy application steps in bitumen.
 3. The method of claim 2 whereinsaid hydrocarbon oil is provided by components inherently present insaid bitumen and/or said dissociated rubber vulcanate.
 4. The method ofclaim 2 wherein said hydrocarbon oil is provided by a hydrocarbon oiladded to said bitumen prior to said mixing step.
 5. The method of claim4 wherein said rubber particles are crumb rubber particles fromautomobile tires.
 6. The method of claim 5 wherein said hydrocarbon oilis one having aromaticity.
 7. The method of claim 6 wherein saidcompatibilizing agent is a liquid rubber capable of compatibilizing saidbitumen and liquid products of said dissociation process step at bitumenprocessing conditions of about 100° to about 300° C.
 8. The method ofclaim 7 wherein said liquid rubber has a molecular weight of about 300to about 60,000.
 9. The method of claim 8 wherein said liquid rubber ispolybutadiene or a polybutadiene-based copolymer.
 10. The method ofclaim 7 wherein said liquid rubber is employed in an amount of about0.01 to about 10 wt % of the bitumen.
 11. The method of claim 10 whereinsaid liquid rubber is used in an amount of about 0.1 to about 3 wt %.12. The method of claim 9 wherein said polybutadiene is anamine-functionalized polybutadiene.
 13. The method of claim 1 includingcross-linking by means of a cross-linking agent, said compatibilizingagent, bitumen and dissociated rubber particles.
 14. The method of claim1, wherein further rubber vulcanate particles are added to thecomposition resulting from said method and, optionally, cross-linking iseffected to stabilize said further rubber vulcanate particles, with orwithout partial dissociation thereof in said composition, againstseparation from the bitumen.
 15. The method of claim 1, wherein apolyolefin is dispersed in the bitumen composition resulting from saidmethod and the dispersed polyolefin particles are stabilized againstseparation by progressive coalescing by steric stabilization by saiddissociated rubber vulcanate network.
 16. The method of claim 1 whereinsaid energy application step is effected for a time which results in anycarbon black particles released from the rubber particles remainingdispersed and resistant to sedimentation after storage of said bitumencomposition at 140° C. for 2 days.
 17. The method of claim 14 whereinsaid energy application step is effected to provide partial dissociationof the further rubber vulcanate particles, and wherein saidcross-linking step is effected to stabilize the dissociated furtherrubber vulcanate particles against separation from said bitumen.
 18. Themethod of claim 17 wherein said cross-linking agent is sulfur, a sulfurdonor or sulfur and accelerator.
 19. The method of claim 18 wherein saidcross-linking agent is employed in an amount of about 0.05 to about 0.5wt %.
 20. The method of claim 19 wherein said cross-linking agent isemployed in an amount of about 0.2 to about 3 wt. %.
 21. The method ofclaim 17 which is carried out to form a bituminous composition whichcontains about 25 to about 80 wt % dispersed stabilized rubber for useas a masterbatch for dilution with a further quantity of bitumen to forma bituminous composition for asphalt applications.
 22. The method ofclaim 21 wherein said masterbatch is compounded with other bituminouscomposition components, including fillers and polymers, and thecompounded composition is pelletized to produce a pelletizedcomposition.
 23. The method of claim 17 which is carried out to form abituminous composition for utilization in asphalt applications.
 24. Themethod of claim 17, wherein a functionalized monomer is incorporatedinto the bitumen composition.
 25. A method for forming a bitumencomposition, which comprises:mixing rubber vulcanate particles with ahydrocarbon oil to effect softening and swelling of rubber particles,applying thermal energy and mechanical energy to said softened andswollen particles to effect at least partial dissociation of a rubbervulcanate network of the rubber vulcanate particles, dispersing said atleast partially dissociated rubber vulcanate network in bitumen havingat least one compatibilizing agent in said bitumen sufficient toincorporate treated rubber from said at least partially dissociatedrubber vulcanate into said bitumen, effecting one or more additionalincremental loadings of rubber vulcanate particles to the at leastpartially dissociated rubber vulcanate network-containing particles andeffecting said thermal energy and mechanical energy application step oneach such additional incremental loading of rubber particles to effectat least partial dissociation of a rubber vulcanate network thereof, andeffecting said thermal energy and mechanical energy application stepuntil all the rubber vulcanate particles have become dissociated to theextent that there is no discernible dispersed phase of rubber vulcanateparticles as determined by the absence of sedimentation of rubbervulcanate particles after storage of said bitumen composition at 140° C.for 2 days.
 26. The method of claim 25 wherein said one or moreadditional incremental loadings of rubber particles is effected toprovide a loading of treated rubber of about 25 to about 80 wt %. 27.The method of claim 25 wherein said dispersing of said at leastpartially dissociated rubber vulcanate network in bitumen is effected byeffecting said mixing and energy application steps in bitumen.
 28. Themethod of claim 27 wherein said rubber particles are crumb rubberparticles from automobile tires.
 29. The method of claim 28 wherein saidhydrocarbon oil is one having aromaticity.
 30. The method of claim 29wherein said compatibilizing agent is a liquid rubber capable ofcompatibilizing said bitumen and liquid products of said dissociationprocess step at bitumen processing conditions of about 100° to about300° C.
 31. The method of claim 30 wherein said liquid rubber has amolecular weight of about 300 to about 60,000.
 32. The method of claim31 wherein said liquid rubber is polybutadiene or a polybutadiene-basedcopolymer.
 33. The method of claim 31 wherein said liquid rubber isemployed in an amount of about 0.01 to about 10 wt % of the bitumen. 34.The method of claim 33 wherein said liquid rubber is used in an amountof about 0.1 to about 3 wt %.
 35. The method of claim 32 wherein saidpolybutadiene is an amine-functionalized polybutadiene.
 36. A bituminouscomposition, comprising:a continuous bitumen phase, a dispersed phasecomprising treated rubber having a dissociated rubber vulcanate networkdissociated to the extent there are no discernible dispersed rubberparticles as determined by the absence of sedimentation of rubberparticles from the bitumen and composition upon storage of saidbituminous composition at 140° C. for 2 days, and a compatabilizationagent.
 37. The bituminous composition of claim 36 further comprising aliquid rubber and additional rubber particles dispersed in said bitumenphase and stabilized against separation by sedimentation from saidbitumen phase by cross-linking between said liquid rubber, bitumen anddissociated rubber vulcanate network.
 38. The bituminous composition ofclaim 37 wherein said dispersed rubber particles are at least partiallydissociated to an at least partially dissociated rubber vulcanatenetwork.
 39. The bituminous composition of claim 36 further comprising aliquid rubber and polyolefin particles dispersed in said bitumen andstabilized against separation by progressive coalescence from saidbitumen phase by cross-linking between said liquid rubber, bitumen anddissociated rubber vulcanate network.
 40. The bituminous composition ofclaim 37, 38 or 39 wherein said liquid rubber comprises a polybutadienehaving a molecular weight of about 300 to about 60,000 and saidcross-linking is effected using sulfur.
 41. The bituminous compositionof claim 40 wherein said polybutadiene is an amine-terminatedpolybutadiene.